Introduction
Ozone layer is naturally evolved a layer made up of atomic oxygen with molecular oxygen and covers a big area in stratosphere. The distinct function of the ozone layer is to absorb ultraviolet wavelengths coming from the solar waves. The collision of ozone occurs because of several other atmospheric molecules and UV radiations (Tabin, 2008).
O3+ UV >>> O2 + O
O3 + O >>> 2O2
The maintenance of the ozone layer is very necessary as through absorbing the solar radiation Ozone establishes the thermal organization of the stratosphere as well as the ecological scaffold for survival on the Earth's surface. Reduction in ozone results in amplified ultraviolet transmission that has bad effects on the health of living (Tabin, 2008).
History of Ozone Depletion
In late 70’s scientists observed a noticeable decline, almost 60% in the quantity of stratospheric ozone over Antarctica during spring season. Satellite measurements have revealed that a continuous decrease of 3% is being measured every year since 1978. During the late 90’s, this loss has augmented manifold every year in the month of august and September. Often the recordings of some years had reached up to 50% below to the amount noticed prior months.
The main reason behind this loss is human releases Chlorofluorocarbons (CFCs) (Solomon, 1999).
It is used as a propellant in spray cans cleaners for electrical devices, to develop bubbles in styrofoam and as a sterilant in hospital equipments. In 1928, General motors Corporation created CFC and replaced toxic refrigerant Ammonia with it. In 1987, a Montreal Protocol was launched in which various countries gathered and emphasize on the necessity of the reduction and elimination of CFCs from the environment (Tabin, 2008).
Systematic measurements of global ozone layer worried the world, and it has appeared as one of the major universal scientific and environmental subject of the 20th century (Solomon, 1999).
Decreasing patterns in ozone are obvious and variable based on region to region. But the behavior on Antarctic is astonishing and unexpected. The ozone depletion record of Arosa, Switzerland in 1920’s set a mark on Ozone history (Solomon, 1999; Andersen & Sarma, 2012).
Montreal protocol has been corrected twice, in 1990 and 1992 to fasten its reduction procedure. In 1996 around 161 countries took part in this protocol and agreed on a 100% decline in the manufacturing and use of CFCs. For the accomplishment of treaty the developed countries were given the year 1996 while developing countries were given more time to the year 2010, to control the production of CFCs (Tabin, 2008). The decided dates for CH3CC13 controls in the developing countries are a freeze in 2003 and a complete phase out by 2015 (Calm & Didion, 1998).
Role of CFC:
The literature is filled with the conceptual and historical understanding of the destruction procedures that control stratospheric ozone, and it has considerable involvement of human utilization of chlorofluorocarbons (CFCs) (Andersen & Sarma, 2012). The chemistry behind this depletion starts with the upward drift of CFCs layer on the earth surface; towards the stratosphere where the UV radiation from the sun decomposes these CFCs and releases Cl. The released Cl attacks the ozone molecule and transforms it into oxygen.
Cl + O3 = Cl + O2
ClO + O = Cl + O2
A chlorine atom can substitute one lac ozone molecules in an instance. Chlorine removal and neutralization in the stratosphere occurs in two reactions:
ClO + NO2 = ClONO2
CH4 + Cl = HCl + CH3
Polar stratospheric clouds rich in nitrogen and sun rays assist a reaction series that prolongs the reactive life of chlorine in the atmosphere. These clouds need around -85O C temperature for the formation. Such conditions appear in the winter and early spring season over Antarctica. The origin of the ozone hole this region is a resultant incidence because of the shift of this region and the clouds are less frequent in Arctic stratosphere (Tabin, 2008).
Though the Montreal protocol has worked well, but now the thickness of this protective layer as not been much effective and thick as it used to be. A number of other air pollutants are responsible for the destruction and harm to the environment. Most of them are combustion products from space heating, power generation, and motor vehicles, and Human-made chlorofluorocarbons as refrigerants (Prinn et al., 2000). Previously several other substances were used as refrigerants but due to increased demand of refrigerant, scientist tried to develop a new substance with high performance. Therefore in 1875 the firstly selected CFC was Di-elene (1-2, dichloroethane) for a centrifugal machine (Calm & Didion, 1998).
The consequences of strong UV radiation involves skin cancer, cataract, immune system weakening, as well as impacts on crops production is also apparent. The highly affected populace is living in the southern hemisphere, like Australia, New Zealand, South Africa and Patagonia.
Australia has 75% inhabitants suffered from skin cancer (Tabin, 2008).
The CFCs expenditure and production of most of the CFCs include various types, including carbon tetrachloride (CC14) and CH3CCl3 (Solomon, 1999)
CFCs have been the best refrigerants for more than 40 years until the research found them as the main factor in ozone depletion. Emissions of the substitutes of CFCs, such as Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons (HFCs) are also rising. The atmospheric trends set by methane are also attention grabbing for environmentalists. CH4 has a very significant role in the troposphere chemistry where it provide a sink to free hydroxyl radicals (OH) and releases carbon monoxide (Prinn et al., 2000)
Various photochemical theories were given explaining depletion of the ozone. An oxygen-based chemical scheme was firstly given by Chapman. His works laid the foundation of odd Oxygen concept. Chapman chemistry has been accepted and described the cause of depletion very closely. 02 + h ν → 2O
O + O2 + M → O3 + M
03 +h ν → O2 + O(1D)
O (1D) + M → O + M
03 + h ν → O2 + O
O+O+ M →O2 + M
O + O3 → 2O2 . (Solomon, 1999)
After the forty years of Chapman's revolutionary approach, researchers proposed that hydrogen and nitrogen are also involved in the ozone depletion chemistry. These two species are capable of destroying the ozone through odd oxygen in a catalytic fashion. In 1947, it was explored that chlorine is also involved in ozone destruction in the catalytic manner. Most astonishing point was the identification of man-made CFCS as the key source of destroying stratospheric chlorine (Calm & Didion, 1998).
Ozone depletion is a very concerning issue of the current time and a big cause of global warming. Environmentalists and governing panels are launching effective protocols to fight this issue and a complete removal of CFCs from the atmosphere.
References
Andersen, S. O., & Sarma, K. M. (2012). Protecting the ozone layer: the United Nations history.
Earthscan.
Calm, J. M., & Didion, D. A. (1998). Trade-offs in refrigerant selections: past, present, and
future. International Journal of Refrigeration, 21(4), 308-321.
Prinn, R. G., Weiss, R. F., Fraser, P. J., Simmonds, P. G., Cunnold, D. M., Alyea, F. N., &
McCulloch, A. (2000). A history of chemically and radiatively important gases in air
deduced from ALE/GAGE/AGAGE. Journal of Geophysical Research: Atmospheres
(1984–2012), 105(D14), 17751-17792.
Solomon, S. (1999). Stratospheric ozone depletion: A review of concepts and history.
Reviews of Geophysics, 37(3), 275-316.
Tabin, S., (2008).Global Warming: The Effect Of Ozone Depletion. APH Publishing.
